The present invention relates to a surveying instrument, and in particular, to a surveying instrument with a tracking function.
As a surveying instrument for measuring a distance, a horizontal angle and a vertical angle, a surveying instrument provided with a tracking function has been known in the past. In this type of the surveying instrument, an object reflector (target) such as a corner cube is collimated by a collimating telescope provided on the surveying instrument. A tracking light is projected from the collimating telescope, and when the target is moved, a reflection light from the target is received and the target can be automatically tracked.
Normally, in a surveying instrument with the tracking function, no operator is assigned on a surveying instrument side. A target is supported by a surveying operator, and the target is moved by the surveying operator for each measuring point. In case a moving speed of the target exceeds a following speed of the surveying instrument and the target goes out of a visual field of a collimating telescope or in case an obstacle such as a tree, a vehicle, a person, etc. temporarily comes into a space between the surveying instrument and the target, and the obstacle intercepts an optical path of the collimating telescope, the surveying instrument cannot receive a reflected light from the target, and an automatic tracking operation may be interrupted.
The reason for this is that, in a collimating telescope generally in use, a field angle (an angle of view) is as small as about 1° and a range to detect the reflection light for purpose of a tracking is too narrow.
When the tracking of the target is interrupted, the surveying instrument starts an operation to search the target. In the searching operation, the collimating telescope is rotated within a predetermined range in up-to-bottom direction and in left-to-right direction while the tracking light is projected for scanning and the target is detected.
As described above, the field angle of the collimating telescope is small. In order to re-detect the target, it is necessary to have a finer scanning pitch and to increase the number of the scanning operations.
For this reason, when the tracking is interrupted, much time is required for the purpose of detecting the target again and for starting the tracking operation. Further, under working conditions where the optical path is frequently intercepted by the obstacle, there are problems in that a working efficiency of the measurement operation is extremely decreased.
The surveying instrument provided with the tracking function is disclosed in JP-A-07-198383, JP-A-2000-346645, and JP-A-2004-170354.